Multispeed hydraulic or pneumatic device

ABSTRACT

A hydraulic or pneumatic device is provided with a cylinder and piston system for providing a rapid stroke and a power stroke. The piston part of said system comprises a piston-rod like plunger piston, which at its lower end slidingly surrounds a tube extending upwardly from, but not secured to the bottom of the cylinder. The cylinder is also provided with two working chambers, which at least partly peripherically surround said piston. Passages are formed in said piston and in said tube for connection of the two working chambers.

United States Patent [191 Bryntse et a1.

MULTISPEED HYDRAULIC OR PNEUMATIC DEVICE Inventors: Anders Ivar Bryntse,Mjolby; Karl Erik Berkestad, Linkoping, both of Sweden AB Bygg-ochTransportekonomi (BT), Mjolby, Sweden Filed: Mar. 16, 1973 Appl. No.:342,216

Assignee:

Foreign Application Priority Data Mar. 24, 1972 Sweden 3859/72 US. Cl91/411 A, 92/152, 60/97 H Int. Cl. .L F15b 11/16 Field of Search 91/411A, 412; ,92/109,

References Cited UNITED STATES PATENTS Stephens 60/97 H ux Aug. 13, 19742,284,228 5/1942 Page 60/97 H X 3,134,232 5/1964 Barosko 91/412X PrimaryExaminerEdgar W. Geoghegan Attorney, Agent, or Firm-Alter, Weiss,Whitesel &

Laff 5 7] ABSTRACT A hydraulic or pneumatic device is provided with acylinder and piston system for providing a rapid stroke and a powerstroke. The piston part of said system comprises a piston-rod likeplunger piston, which at its lower end slidingly surrounds a tubeextending upwardly from, but not secured to the bottom of the cylinder.The cylinder is also provided with two working chambers, which at leastpartly peripherically surround said piston. Passages are formed in saidpiston and in said tube for connection of the two working chambers.

7 Claims, 1 Drawing Figure MULTISPEED HYDRAULIC OR PNEUMATIC DEVICE Thepresent invention relates to a hydraulic or pneumatic device including acylinder and piston system for providing a rapid stroke and a powerstroke, in which system the piston slidingly surrounds a tube extendingfrom the bottom of the cylinder. The device is especially although notexclusively intended for use in trucks for handling goods, e.g. pallettrucks.

Known pallet trucks have a fixed ratio between the movement of the pumppiston and the movement of the lift piston. The ratio is so chosen that,with maximum load on the pallet truck, it is possible, via a lever sys'tern, manually to effect the movements of the pump piston. The ratio istherefore not so effective when lifting light loads or when the truck isunloaded. An unloaded conditions occurs before the pallet truck,inserted under the load, has been pumped up into engagement with theload. The height of this unloaded lift movement is dependent upon theshape and dimensions of the pallet and usually varies between 15 and 45mm. A ratio often used in pallet trucks is so chosen that one pumpstroke gives about mm movement of the lift piston.

The main object of the present invention is to provide a movement of thelift piston, which movement is automatically dependent on load, therebyeliminating most of the disadvantage mentioned above.

In other connections, devices are known, in which a pressuretransmission medium (such as a hydraulic or pneumatic fluid) is suppliedto the cylinder through its bottom and through a tube fixed tothisbottom. The lift piston has a central bore for sealingly andslidingly around the tube. In this way, a further working chamber isprovided inside the piston, which mounting the piston working chamber isused to effect a rapid lift. However, in this case an extension of thecylinder downwards is necessary to enable the medium to be suppliedthere.

The basic conception of the present invention is to give the cylindertogether with .theliftpiston such a form, that two outer workingchambers are formed in relation to the piston. This gives an opportunityto supply the pressure transmission medium almost everywhere along thewhole length of the cylinder. Furthermore the construction will besimple and economical with a minimum number of movable parts. The methodis especially suitable for cylinders having a relatively short length ofstroke, e.g. cylinders in pallet trucks. The inventive supply of themedium makes it possible for a cylinder according to the invention tohave outer dimensions in full conformity with conventional well testedand well motivated constructions.

According to the invention, the piston comprises a piston-rod likeplunger piston workingin and being at least partly periphericallysurrounded by two working chambers formed in the associated cylinder.These working chambers are connected by a passage formed in the plungerpiston.

A preferred embodiment of the invention will now be described by way ofexample with reference to the accompanying drawing, which is alongitudinal cross section view showing the piston and cylinderconstructed according to the invention.

In the drawing, a cylinder housing 1 includes a piston-rod like plungerpiston 5 with uniform diameter.

This piston is sealingly guided in relation to the cylinder housing 1 bymeans of upper and mid wall section guides 3 and 4 and is arranged torun easily therein.

Mid wall section 4 divides the cylinder into two peripheral chambers 14and 16. The piston 5 is further provided with a central bore forming a.working chamber 7. In this bore is slidingly mounted a tube 2, whichextends upwardly from the bottom of the cylinder housing 1, but is notsecured thereto.

Flow control means are pivoted in the form of the piston bore 7, theinner passage through the tube 2, passages 8 and 10 in the piston S,passages 6 and 13 in the tube 2, a ball 11 and a valve seat 12, whichenables the pressure. transmission medium to pass from a first workingchamber 14 to another chamber 15, but precludes flow in the oppositedirection, since the ball 11 then seals itself against the seat 12.

The cylinder housing 1 also contains a reservoir 16 for the pressuretransmission medium and passages 17 and 18, which permit the pressuretransmission medium to flow from the reservoir 16 into the workingchamber 14, but not in the opposite direction, since a valve ball 19then seals itself against a seat 20.

The cylinder housing contains a further passage 21, which can beconnected through a valve system known per se, but not disclosed here,to the pump (not shown) during the pumping up and to the reservoirduring the lowering.

Furthermore the cylinder housing 1 contains a valve in a bore.291 thevalve includes a hole 22, a ball 23, a piston 24, an O-ring 25, a spring26 and a screw plug 27, provided with a hole 28. The piston 24 with theO- ring 25 is easily movable in relation to bore 29. When the springloaded valve is opened, the passage 21 is connected to the workingchamber 14 via the hole 22, the ball 23 and a passage 30.

The operation of the parts here above described is as follows:

Inorder to extend the piston 5, the pressure transmission medium ispressed, via the valve system known per se, through the passage 21 intothe working chamber 15 and through the passages 8 and 10 into the bore7, the ball 11 thereby being sealingly pressed against the seat 12 andthe tube 2 being pressed against the bottom of the cylinder housing 1.At this time, there is no communicationbetween the passage 21 and theworking chamber 14 because it is closed by the ball 23, which the spring26 and the piston24 are sealingly pressing by against the opening of thehole 22. Thus, the pressure of themedium acts only inside the bore 7.Therefore, the piston 5 will receive a large movement in relation to thequantity transmission medium supplied to the bore 7. The pressuretransmission medium will also be drawn from the reservoir 16 through thepassage 17, past the ball 19 and via thev passage 18 into the workingchamber 14. lf the piston 5is sufficiently loaded, the pressure of themedium arrives at a value such that the total power acting on thesectional area of the hole 22 exceeds the spring power 26. Then the ball23 is pressed from its seat and the pressure transmission medium hasfree access to the chamber, .which is formed by the bore 29 and thepiston 24, and from this chamber via the passage 30 to theworkingchamber 14. The ball 19 is now forced against its seat 20 to prevent thepressure medium fromflowing into the reservoir 16. The pressure of themedium is then immediately decreased to a value, which corresponds tothe load on the piston 5 divided by the sectional area of that piston.The screwplug'27 is provided with the hole 28 in order to ensure thatatmospheric pressure always exists on the surface of the piston 24 whichfaces the spring 26.

The above described change-over device can use other means than thedescribed valve 23 29, (e.g. valving may be accomplished through a smallslot or the like), the pressure equalizing being made at a certainpiston-rod load and pump speed. Such a system, however, is dependent onthe viscosity of the pressure medium and causes losses through the chokewhich the slot represents. The change-over valve 23 29 is nonsensitiveto viscosity differences and can be substantially loss free.

In order to lower the piston 5, the passage 21 is connected to thereservoir 16 via the valve system, known per se, there is substantiallyatmospheric pressure in reservoir 16. This means that the pressuretransmission medium in the working chamber 15, which is underover-pressure, can freely flow to the reservoir 16. The medium in theworking chamber 14 is also able to flow to the reservoir 16 through thepassages 6 and 13, past the ball 11, the inner passage through the tube2, the bore 7, the passages 8 and 10, the working chamber and thepassage 21.

The cylinder'can be driven with either a gas or liquid as the pressuretransmission medium.

We claim: I

l. A hydraulic or pneumatic lifting device comprising a piston andcylinder system for providing a rapid stroke and a power stroke, thepiston of said system comprising a piston-rod like plunger having alower end with a central co-axial bore surrounding a tube extendingupwardly from the bottom of the cylinder of said system, said pistonfurther being provided with two pressure areas located in two separateand axially aligned working chambers longitudinally spaced apart alongthe direction of the piston stroke, said cylinder being in communicationwith both of said pressure areas of said piston and having upper and midwall sections in direct contact with the outer surface of said pistonthereby forming two peripheral chambers around said piston, one of saidperipheral chambers being a first working chamber and the other of saidperipheral chambers being in communication with the other workingchamber in said bore, each of said working chambers being provided witha supply line for a pressure transmission medium, one of said lineshaving therein valve means controlled by the medium transmissionpressure, passage ways for said pressure transmission medium beingformed in said piston and in said tube for interconnecting the twoworking chambers with each other, and spring biased control meansinserted in said passage ways to enable the pressure transmission mediumto flow between said working chambers in only one direction and precludeflow in an opposite direction.

2. A device according to claim 1, wherein said tube is floatinglyresting on the bottom of said cylinder.

3. The device of claim 2 and means for normally directing all of saidpressure transmission medium into the other of said peripheral chambersto act upon a first of the pressure areas in the communicating workingchambers and on said flow control means for normally precluding saidflow in said opposite direction.

4. The device of claim 3 and means for diverting at least a part of saidpressure transmission medium from said other peripheral chamber and intothe other combined one peripheral working chamber and where saidpressure transmission medium acts upon said flow control means to enablesaid pressure transmission means to flow in said one direction.

5. The device of claim 4 and means whereby said diverting means isoperated responsive to pressure in the first peripheral chamberexceeding said spring bias acting on said flow control means.

6. The device of claim 5 wherein the relative dimensions of the twopressure areas are such that said plunger piston has an initial rapidstroke before said flow control means enables said flow in said onedirection, followed by a power stroke after said enabled flow begins insaid one direction.

7. The device of claim 1 and spring biased flow enabling meansassociated with said tube, means responsive to the pressure in one ofthe working chambers exceeding said spring bias by at least apredetermined amount for diverting at least a part of said pressuretransmission medium from a working chamber and into the other of saidworking chambers where it acts upon said flow enabling means and enterssaid tube to act upon another pressure area.

1. A hydraulic or pneumatic lifting device comprising a piston andcylinder system for providing a rapid stroke and a power stroke, thepiston of said system comprising a piston-rod like plunger having alower end with a central co-axial bore surrounding a tube extendingupwardly from the bottom of the cylinder of said system, said pistonfurther being provided with two pressure areas located in two separateand axially aligned working chambers longitudinally spaced apart alongthe direction of the piston stroke, said cylinder being in communicationwith both of said pressure areas of said piston and having upper and midwall sections in direct contact with the outer surface of said pistonthereby forming two peripheral chambers around said piston, one of saidperipheral chambers being a first working chamber and the other of saidperipheral chambers being in communication with the other workingchamber in said bore, each of said working chambers being provided witha supply line for a pressure transmission medium, one of said lineshaving therein valve means controlled by the medium transmissionpressure, passage ways for said pressure transmission medium beingformed in said piston and in said tube for interconnecting the twoworking chambers with each other, and spring biased control meansinserted in said passage ways to enable the pressure transmission mediumto flow between said working chambers in only one direction and precludeflow in an opposite direction.
 2. A device according to claim 1, whereinsaid tube is floatingly resting on the bottom of said cylinder.
 3. Thedevice of claim 2 and means for normally directing all of said pressuretransmission medium into the other of said peripheral chambers to actupon a first of the pressure areas in the communicating working chambersand on said flow control means for normally precluding said flow in saidopposite direction.
 4. The device of claim 3 and means for diverting atleast a part of said pressure transmission medium from said otherperipheral chamber and into the other combined one peripheral workingchamber and where said pressure transmission medium acts upon said flowcontrol means to enable said pressure transmission means to flow in saidone direction.
 5. The device of claim 4 and means whereby said divertingmeans is operated responsive to pressure in the first peripheral chamberexceeding said spring bias acting on said flow control means.
 6. Thedevice of claim 5 wherein the relative dimensions of the two pressureareas are such that said plunger piston has an initial rapid strokebefore said flow control means enables said flow in said one direction,followed by a power stroke after said enabled flow begins iN said onedirection.
 7. The device of claim 1 and spring biased flow enablingmeans associated with said tube, means responsive to the pressure in oneof the working chambers exceeding said spring bias by at least apredetermined amount for diverting at least a part of said pressuretransmission medium from a working chamber and into the other of saidworking chambers where it acts upon said flow enabling means and enterssaid tube to act upon another pressure area.